For viewers who had never heard of Alex Jones before Sunday evening, Megyn Kelly’s much-hyped interview with him on NBC did not paint a flattering picture.

In a 17-minute segment — which had generated hours of commentary and a raft of protests before it aired — Ms. Kelly repeatedly challenged Mr. Jones, the conspiracy theorist, Infowars founder and influential right-wing personality.

She pressed him on his baseless claims that the Sandy Hook school shooting was a hoax. She confronted him about describing teenage victims of the terror attack in Manchester, England, in May as “liberal trendies.” And she described his behavior as “reckless accusation, followed by equivocations and excuses.”

Ms. Kelly’s solemn and scolding tone — “That doesn’t excuse what you did and said about Newtown,” she told Mr. Jones at one point as he tried to explain his views on Sandy Hook — may placate some who objected when the former Fox News anchor announced her feature on Mr. Jones.

Media Matters, the liberal advocacy site that had raised alarms about NBC’s decision to cover Mr. Jones, called the segment “a well-edited investigation of the dangers posed by an unstable megalomaniac with millions of loyal fans.”

Others said Ms. Kelly did not go far enough in her interrogation, or argued that the mere fact that the segment was being aired, regardless of its handling, would only serve to raise Mr. Jones’s renown. “Still a win for him; boosts his profile,” the media critic Margaret Sullivan wrote on Twitter.

Executives at NBC — who re-edited Ms. Kelly’s segment throughout the week and have gambled millions of dollars on her success — were likely to be feeling some relief. In recent days, relatives of Sandy Hook victims had denounced the network; the NBC affiliate in Connecticut announced it would not air the segment; and critics like Mayor Bill de Blasio of New York said Ms. Kelly was abetting Mr. Jones with her reporting.

A photograph released by Mr. Jones last week showed Ms. Kelly smiling with him during their time together, heightening skepticism that she would be tough on him.

To drive home Mr. Jones’s relevance, Ms. Kelly noted his millions of listeners, including one prominent fan: President Trump. She showed clips of Mr. Trump, on the campaign trail last year, reciting talking points from Mr. Jones and making a friendly appearance in a video on Mr. Jones’s website.

In a voice-over, Ms. Kelly said that Mr. Jones’s message “has caused enormous pain,” and in the interview, she read aloud to Mr. Jones his statements about the Sandy Hook murders and asked: “All of the parents decided to come out and lie about their dead children?”

Mr. Jones stammered and often sidestepped Ms. Kelly’s questions. But he stuck to his argument that he was playing a “devil’s advocate.”

“I tend to believe that children probably did die there,” he said. “But then you look at all the other evidence on the other side.”

Ms. Kelly’s rejoinder came in a voice-over: “Of course, there is no ‘evidence on the other side.’”

Jonathan Klein, a former CNN president, said in a telephone interview on Sunday night that “there’s no question that it was more than legitimate for NBC News to do this interview.”

“One of the main purposes of journalism is to expose characters like Alex Jones and hold them accountable, especially when they hold such attention from the president of the United States,” Mr. Klein said.

Mr. Jones, who has called Ms. Kelly a partisan intent on smearing his image, offered his own rebuttal on Sunday night in a live broadcast with one of Mr. Trump’s longtime advisers, Roger J. Stone Jr.

“You people are desperate,” Mr. Jones said, addressing what he terms the mainstream media. “And you think destroying me will help you.”

In recent days, Ms. Kelly contacted relatives of Sandy Hook victims about appearing on her segment about Mr. Jones; several declined, although Neil Heslin, whose son died in the massacre, granted an interview. Other Sandy Hook relatives said in interviews on Sunday evening that they had decided not to watch.

“I didn’t even have to think about it,” said Jillian Soto, whose sister Victoria, a first-grade teacher, died in the shooting. She added: “Giving Alex Jones this interview is giving these crazy people a platform. They’re happy about this. They’re excited about the exposure that they’re getting and nobody seems to care about the harm that it’s doing to others.”

Erica Lafferty, whose mother, Dawn Hochsprung, was the principal of Sandy Hook and was also killed, said that Mr. Jones “has harassed and tormented our families for the past four and a half years.” Both women said they had been attacked on social media and had been confronted in person by people who accused them of perpetuating a hoax.

Ms. Kelly, a former star on Fox News, is a new face for NBC viewers. On Sunday, her program concluded with an appearance by the veteran anchor Tom Brokaw, who offered what amounted to an implicit endorsement of her work from a trusted voice.

“We cannot disrupt the irrational spread of hate and division by instantly, blindly blaming the other side, or looking away,” Mr. Brokaw said.

Kristin Hussey contributed reporting.

A version of this article appears in print on , on Page B6 of the New York edition with the headline: Kelly Presses Conspiracy Theorist in Edited Interview. Order Reprints | Today’s Paper | Subscribe